Trace fossils and marine-nonmarine cyclicity in the Fountain Formation (Pennsylvanian: Morrowan/Atokan) near Manitou Springs, Colorado

Abstract

The Lower Pennsylvanian (Morrowan/Atokan) portion of the Fountain Formation in the Manitou Springs, Colorado, area commonly has been interpreted as a subaerial alluvial fan. However, approximately 12 marine-nonmarine cycles, each represented by a discrete progradational sequence, have been recognized within the lower third of the Fountain Formation in this area. The typical cycle is composed of six lithofacies: 1) transgressive-lag conglomerate; 2) offshore mudstone; 3) hummocky crossbedded sandstone; 4) planar crossbedded granular sandstone; 5) low-angle, crossbedded, coarse-grained sandstone; 6) lenticular conglomeratic sandstone. Only lithofacies 6 is nonmarine (alluvial) in origin. Two diverse trace-fossil assemblages (totalling 18 ichnogenera and 20 ichnospecies) within the Fountain Formation are restricted to the marine portions of the section, or to those portions within 1 m below marine-deposited strata. The assemblage includes Arenicolites carbonarius, ?A. ichnosp., Aulichnites parkerensis, two types of Chondrites, ?Conostichus broadheadi, ?Crossopodia ichnosp., Curvolithus manitouensis (ichnosp. nov.), Eione ichnosp., Lockeia ichnosp., Macaronichnus segregatis, Palaeophycus heberti, Palaeophycus striatus, Planolites beverleyensis, Psammichnites plummeri, Rhizocorallium irregulare, ?Skolithos ichnosp., Taenidium serpentinum, ?Teichichnus ichnosp., ?Thalassinoides ichnosp., ?Zoophycos ichnosp., and several unnamed traces.Trace fossils in the Fountain Formation can be used as indicators of sedimentary processes (e.g., rates of deposition, energy regime). Trace-fossil composition changes along a roughly south-to-north, nearshore-to-offshore gradient, generally reflecting increased influence and duration of normal-marine sedimentation. Ichnotaxa present and their distributions within marine strata in the lower part of the Fountain Formation suggest that they belong to the Curvolithus ichnoassemblage, which has been shown to indicate high sedimentaiton rates in relatively nearshore shelf settings. The Curvolithus ichnoassemblage can be subdivided into Macaronichnus-dominated and Curvolithus-dominated parts. Macaronichnus-dominated portions of the Fountain Formation indicate generally higher wave-energy sedimentation as compared with Curvolithus-dominated portions.

Ichnostratigraphy of the Ediacaran-Cambrian boundary: new insights on lower Cambrian biozonations from the Soltanieh Formation of northern Iran

“…Planolites is interpreted as feeding burrows (fodinichnia) of deposit-feeders (Pemberton and Frey, 1982), and ranges in age from Cambrian to Holocene (Häntzschel, 1975;Mángano and Buatois, 2014). Planolites is found in almost every depositional environment (Pemberton and Frey, 1982 Remarks.-There is general agreement that the ichnogenus Olivellites Fenton and Fenton, 1937 is a junior synonym of Psammichnites (Chamberlain, 1971;D'Alessandro and Bromley, 1987;Maples and Suttner, 1990;Seilacher, 1997;Zhu, 1997;Mángano et al, 2002a Mángano and Buatois, 2016). Psammichnites is distinguished from Didymaulichnus by lack of median groove on the lower side and by its overall more complex internal structure (Seilacher, 2007).…”

Wetland-Dryland Vegetational Dynamics in the Pennsylvanian Ice Age Tropics

“…There also are examples of assemblages composed entirely of wetland species, the more typical and diverse of which are from older Pennsylvanian strata; these are, in almost all instances, parautochthonous to autochthonous and thus not likely to reveal more than very local vegetation. Most such floras have not been published (we have a number of examples in the National Museum collections), but published examples include floras rich in lepidodendrids and other wetland species from the Mississippian-Pennsylvanian boundary in Arizona (Tidwell et al 1992) and from strata of Atokan age in New Mexico ) and Colorado (Jennings 1980; for a humid-climate interpretation of this deposit, see Mack and Suttner 1977;Maples and Suttner 1990) and a late Desmoinesian-age autochthonous pteridosperm-dominated (Neuropteris ovata) coastal swamp deposit from New Mexico ( fig. 16F, 16G), mentioned above, identified over several square kilometers .…”

A rich ichnofossil assemblage from the Frasnian (Upper Devonian) deposits at Andoma Hill, Onega Lake, Russia

“…-The morphologically simple trace is considered to be a cubichnion of bivalves. For the description of the ichnogenus, its origin and representatives see, e.g., Maples & Suttner (1990), Schlirf et al (2001).…”